1. Field of the Disclosure
The present disclosure relates in general to valve bonnets and more particularly, to valve bonnet seals for use with oil, gas and other fluids.
2. Description of Related Art
A gate valve has a body with a central chamber that is intersected by a flow passage. A gate moves within the chamber between the open and closed positions. The gate has a hole through it that aligns with the flow passage while in the open position. A stem extends into engagement with the gate for moving the gate between open and closed positions. In one type, the stem has a first end that extends through a bonnet of the valve body assembly and a second end that extends into rotatable engagement with a threaded nut or sleeve secured to the gate. Rotating the stem causes the gate to move linearly. In another type, the stem does not rotate. Instead a threaded nut or sleeve mounted in the bonnet engages the stem, and when rotated, causes the stem to move linearly.
In gate valves, and in other valves with stems that rotate or move linearly, a stem packing is typically located in the bonnet and engages the stem to seal pressure within the chamber. Valves which are designed to work within a defined fire envelope must be capable of providing both high integrity normal operation well control and emergency pressure containment in the event of a fire. A single metal to metal seal that can meet both of these demands can require special coatings and can be very expensive and technically difficult to design and implement, especially on rotary valves. In addition, a single seal does not provide redundancy in the case of the failure of the seal.